The present invention relates to a pump and more particularly to an improvement in a vane-type pump.
A hitherto known pump of this type, namely a vacuum pump to be mounted to a vehicle generator, is shown in FIGS. 1 and 2 of the accompanying drawings. In these drawings reference numeral 1 designates a frame of the vehicle generator, 2 designates a shaft rotatively supported in the bore 1a formed in the frame 1 by means of a bearing 3 fit therein, 2a designates splines formed on the shaft 2 on the free end portion thereof, and 4 designates a rotor splined to the shaft 2 by the splines 2a. The rotor 4 is provided with a number of radial slots 4a at regular angular intervals (in the embodiment shown the number of radial slots 4a is 3), and a rectangular plate-like vane 5 is radially shiftably received in each of the slots 4a. A cylindrical housing 6, open at one end and closed at the other end, has a generally cylindrical inner peripheral surface 6a the center line of which is eccentric with respect to the center line 6 of the shaft 2, i.e. the center line of the rotor 4, the housing 6 being secured to the frame 1 at the open end by a number of fastening bolts 7. A packing 8 is held by the housing 6 within an annular groove formed therein to hermetically seal it to the frame 1, and an oil seal 9 is secured in the bore 1a of the housing 1 so as to abut against the outer surface of the shaft 2 for hermetically sealing an operating chamber 10 of the pump formed within the housing 6 from the outside. A suction port 11 is formed in the housing 6 through its peripheral wall, and a discharge port 12 is similarly formed therein so as to be generally diametrically opposite to the suction port 11, and a lubricant oil feed orifice 13 opens through the end wall of the housing 6 in alignment with the center line 2.sub.1 of the shaft 2, the suction port 11, discharge port 12, and lubricant oil feed orifice 13 being connected to a not-illustrated vacuum tank, oil pan, and lubrication pump, respectively.
The operation of the conventional vacuum pump having such a construction as described above is as follows.
Upon rotation of the shaft 2 in the direction indicated by the arrow, the vanes 5 are urged radially outwards due to centrifugal force applied thereto so that they rotate together with the rotor 4 with the radially outward ends of the vanes 5 abutting against the cylindrical inner peripheral surface 6a of the housing 6. Air is thereby sucked through the suction port 11 and discharged through the discharge port 12, and a pumping action is thus performed. The lubricant oil supplied from the lubricant oil feed orifice 13 to the housing 6 lubricates the surfaces of the radially outward ends of the vanes 5 and the cylindrical inner periphery 6a of the housing 6 and is then entrained with the discharged air to be discharged from the discharge port 12 into the oil pan.
Since the conventional vane-type pump has the construction and operation described above, when the pump is operated at a high velocity or without lubrication, the radially outward ends of the vanes 5 are extraordinally worn due to friction occurring between them and the cylindrical inner periphery 6a of the housing 6, and in the case where the vane 5 is made of carbon, the bonds between the carbon particles at the shifting portion contacting the cylindrical inner periphery of the housing 6 are weakened to cause breaking off of portions of the vane 5, and the durability of the vane 5 considerably deteriorates. For this reason, high-speed operation and operation without lubrication of a pump of this type are difficult.
A vane-type pump of this kind is disclosed in Japanese Laid-Open Utility Model Publication No. 29406/1979, but this conventional pump does not disclose the use of a cylindrical casing disposed between the cylindrical inner periphery of the housing and the rotor, the casing being rotated by the shaft directly or indirectly so that the relative velocity between the cylindrical inner periphery of the casing and the radially outward ends of the vanes which are urged to abut against them is greatly reduced as in the present invention to be described fully hereinbelow.